Men paint an oil containment dome at Port Fourchon, Louisiana, on Tuesday, on Tuesday, May 11, 2010. The first containment dome dropped over an oil leak in the Gulf of Mexico did not stop the leak. (Travis Heying/Wichita Eagle/MCT)

WASHINGTON — Investigators on Tuesday homed in on whether an uncommon sequence of events involving a decision to remove heavy drilling lubricants early from a pipeline may have triggered the sudden upwelling of gas that led to the explosion and sinking of the Deepwater Horizon offshore oil rig.

The topic came up as both Congress and a federal panel in Louisiana opened inquiries into the April 20 explosion, which killed 11 and mangled a deepwater well that continues to spew 210,000 gallons of crude oil into the Gulf of Mexico daily.

As the inquiries opened, the Obama administration announced a major reorganization of the Mineral Management Service, the government agency that oversees offshore drilling. Interior Secretary Ken Salazar said MMS would be split in two, dividing its leasing-royalty collection function from its safety and environment enforcement responsibilities amid growing complaints that the relationship between MMS and the oil industry is too cozy.

Meanwhile, BP announced that the "top hat" it hopes to drop over one of the leaks 5,000 feet below the surface of the Gulf of Mexico had left a Louisiana port where it was being readied. BP said the steel and concrete device would arrive at the Deepwater Horizon site perhaps as early as Tuesday night and might be in place as early as Thursday.

What triggered the explosion that sank the rig and unloosed the flow of crude is critical to understanding not only who to blame for what may become the worst crude oil spill in U.S. history but whether much tougher limitation should be placed on what oil companies can and cannot do when drilling in deep water.

Anthony Gervaso, the engineer aboard a supply ship that was parked near the rig when it exploded, told a Coast Guard inquiry in Kenner, La., that he'd learned from his captain that rig workers pulled from the water had said they'd just start removing the drilling lubricant from the well when gas shot up the pipe and exploded.

Tim Probert, an executive of Halliburton, the subcontractor responsible for placing a cement plug in the well, told senators in Washington that the dense drilling fluid had been pulled from the drilling tube and replaced with much lighter seawater before a cement plug had been set to block gas and oil from coming up the pipeline.

Normally, the procedure would have been to place the plug and then switch out the drilling fluid for sea water. But he said the decision to reverse the process came at the instigation of BP, the well's owner.

The switch, he said, was in accordance with the requirements of the well owner's well construction plan.

The drilling fluid is commonly called mud, but it is a complex and expensive recipe of clay and minerals that is recovered from a well and recycled. For a boring like the Deepwater Horizon project, mud could make up more than 10 percent of the cost of the overall project, potentially in excess of $10 million to $20 million, and mud experts with engineering degrees, one of whom was killed in the explosion, were on hand to oversee its use.

Before a cement plug is installed, muds are the most important and effective way to restrict gasses and fluids held under pressure deep underground.

Probert, asked whether the practice was an unusual sequence of events, told Sen. Jeff Session, R-Ala., that he couldnt answer that question, but that it had been used on multiple occasions in the Gulf of Mexico.

As for who was responsible for determining whether it was a normal sequence of events, both Probert and Steven Newman, the CEO of Transocean, which owned the rig, said it would have been up to BP as the well owner to have conversations with MMS about that.

As the lease operator and the well owner, that falls on BP, Newman said.

Demonstrators in Miami Beach protested the spill Tuesday.

BP American President Lamar McKay told both the Senate Energy and Natural Resources Committee and the Senate Environment and Public Works panel under oath that his company would be responsible for its cleanup.

"We are prepared to clean up and deal with anything that gets on shore and we're prepared to deal with the economic impact," he said.

That pledge left few of the senators satisfied. The chairman of the Senate Energy and Natural Resources Committee, Sen. Jeff Bingaman, D-N.M., said it was not enough to label the spill an "unpredictable and unforeseeable" event.

"If this is like other catastrophic failures of technological systems in modern history whether it was the sinking of the Titanic, Three Mile Island or the loss of the Challenger, we will likely discover that there was a cascade of failures: technical, human and regulatory," Bingaman said.

None of the executives was willing to accept blame for causing the disaster, however.

McKay emphasized that BP had hired Transocean to drill the well, and questioned whether Transocean's blowout preventers — huge devices that sit atop the well under water that are intended to close the drilling pipe in the event of a disaster — had worked properly.

Apart from looking at the causes of the explosion, we are also examining why the blowout preventer _ the BOP, as it's called _ did not work as the ultimate failsafe to seal the well and prevent an oil spill, McKay said.

Drilling had been finished on April 17th, and the well had been sealed with casing and cement, Newman said. For that reason, the one thing we do know is that, on the evening of April 20th, there was a sudden catastrophic failure of the cement, the casing, or both.

Halliburton, the cement contractor responsible for sealing the oil well, put the blame on BP as the owner of the well, saying it simply was following BP's instructions.

McKay declined to address the issue of why the decision was made to pull the drilling lubricants early. He said BP knows there were unusual pressure test readings prior to the explosion but that he was not familiar with the individual procedure on that well.

The investigation is going to look at every piece of the procedure, the directives, the decisions, and the processes that was used, and that -- that investigation is underway, he said. So I've not had a review of that yet.

Asked by Sessions whether a blowout would have been less likely if the mud had not been removed, he responded: "I don't know. I don't know.

Exasperated with their finger-pointing, the top Republican on the Senate Energy Committee, Sen. Lisa Murkowski, R-Alaska, warned the executives that their negligence could harm future offshore drilling in U.S waters and have an impact on the countrys energy policy.

I would suggest to all three of you that we are all in this together, she said. Not only will BP not be out there, the Transoceans wont be there to drill and the Halliburtons wont be there to provide the cementing.

A White House spokesman said Tuesday that like Congress, President Barack Obama has run out of patience with the failure to stop oil from gushing into the Gulf of Mexico.

"The president is deeply frustrated that we have not plugged this leak," Press Secretary Robert Gibbs said Tuesday.

The failure to stop the leak dominated a White House meeting with top aides about the spill on Monday, Gibbs said.

"Secretary Chu is heading to the area and to work with the response team to make sure that we have some of the best and brightest minds down there trying to think through next steps for doing so. But I think the president is deeply frustrated."

(Washburn, of the Charlotte Observer, reported from Kenner, La., McClatchy correspondents Blumenthal and Bolstad from Washington. Contributing to this story were Marc Caputo, of the Miami Herald, in New Orleans, Sara Kennedy, of the Bradenton Herald, in Siesta Key, Fla., Jennifer Lebovich of the Miami Herald in Miami, Geoff Pender of the (Biloxi, Miss.) Sun Herald in Biloxi, and McClatchy correspondents Lesley Clark, Rob Hotakainen and Steve Thomma in Washington.)

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